Solid electrolyte for ReRAM

ABSTRACT

A composition comprising
     (i) a matrix comprising a metal oxide, metal sulphide and/or metal selenide as the matrix material, the metal oxide, metal sulphide and/or metal selenide comprising at least two metals M1 and M2, and   (ii) a metal M3 which is mobile in the matrix.   The atomic ratio of M1 to M2 is within the range of 75:25 to 99.99:0.01;   the valence states of M1, M2 and M3 are all positive;   the valence state of M1 is larger than the valence state of M2;   the valence state of M2 is equal to or larger than the valence state of M3; and   the metals M1, M2 and M3 are different.

RELATED APPLICATIONS

This application is a U.S. national phase application of InternationalPatent Application No. PCT/EP2017/053218 filed on Feb. 14, 2017 andpublished as international Publication No. WO 2017/140647 on Aug. 24,2017. This application claims the benefit of priority to PatentApplication No. 16156125.3 filed in Europe on Feb. 17, 2016, thecontents of which are incorporated in this application by reference.

FIELD OF THE INVENTION

The present invention relates to a composition suitable as a solidelectrolyte for ReRAM, a process for its manufacture and the use thereofas an active switching element in ReRAMs.

BACKGROUND OF THE INVENTION

Non-volatile memory devices are used in a multitude of everydayelectronics, e.g. smartphones, music players, USB-sticks, memory cards,e.g. for digital cameras, solid-state disks (SSDs) etc.

Non-volatile memories such as the so-called EPROM-technology has certainlimits as regards the storage density, access, erase and writing timesmaking it undesirable for the constantly increasing data volume inmodern applications, such as the ones mentioned above.

A further technology for non-volatile memories are resistive switchingmemories which are formed of arrays of resistive switching elements.Each of these elements has two or more stable resistive states.Switching between the states is accomplished by specific voltage pulses.

Resistive switching elements use a “forming process” to prepare a memorydevice for use. The forming process is typically applied at the factory,at assembly, or at initial system configuration. A resistive switchingmaterial is normally insulating, but a sufficient voltage (known as aforming voltage) applied to the resistive switching material will form aconductive pathway in the resistive switching material. Through theappropriate application of various voltages (e.g. a set voltage andreset voltage), the conductive pathways may be modified to form a highresistance state or a low resistance state. For example, a resistiveswitching material may change from a first resistivity to a secondresistivity upon the application of a set voltage, and from the secondresistivity back to the first resistivity upon the application of areset voltage which voltages are usually different from each other.

Two types of ReRAM switching elements are currently under investigation,namely valence change memory (VCM) and electrochemical metallizationmemory (ECM). In VCMs oxygen anions are removed from a metal oxidematrix whereupon the conductivity of the metal oxide matrix increases.In ECMs metal ions are reduced and build filaments within the matrixbetween the two electrodes thereby increasing the electricalconductivity. It has recently been found (cf.http://www.fz-juelich.de/SharedDocs/Pressemitteilungen/UK/DE/2015/15-09-28nnano_reram.html)that in VCMs in addition to the oxygen ion movement also filaments areformed. However, in VCMs elemental oxygen needs to be stored which maymigrate to the surface of the electrode and cause delamination thereof.

In current solid state electrolytes usually amorphous metal oxides areused as a matrix whereby the transport of a metal ion therethrough leadsto built-up and dissolution of a metallic filament between the twoelectrodes attached thereto.

After a multitude of switching processes the structure of the solidstate electrolyte changes leading to separate metallic phases of the ionto be transported and, in turn continuously changes the switchingbehavior of the electrolyte making the switch unusable as memory.Moreover, a high degree of purity is desired in order to suppress sidereactions and phase separations.

Thus, a solid state electrolyte is needed which is not prone to changesin the switching behavior or which at least has a significant lower rateof change thereof due to the charge-state stabilization of the mobileion in the matrix.

SUMMARY OF THE INVENTION

It has been found that this can be achieved by introducing a fixed localcharge compensation element into the crystalline or amorphous matrixwhich has a lower valence state that the metal ion of the matrix.

Hence, the present invention provides various embodiments of acomposition comprising:

-   -   a matrix comprising a metal oxide, metal sulphide and/or metal        selenide as the matrix, the metal oxide, metal sulphide and/or        metal selenide comprising at least two metals M1 and M2, and    -   a metal M3 which is mobile in the matrix,        wherein    -   the atomic ratio of M1 to M2 is within the range of 75:25 to        99.99:0.01, preferably 90:10 to 99.99:0.01;    -   the valence states of M1, M2 and M3 are all positive;    -   the valence state of M1 is larger than the valence state of M2;    -   the valence state of M2 is equal to or larger than the valence        state of M3; and    -   the metals M1, M2 and M3 are different.

The composition is particularly suitable as an electrochemicalmetallization memory (ECM). It has been found that by the abovecomposition, the switching behavior of the composition when used in aresistive switching material can be significantly improved. It iscurrently believed that the negative localized charge caused by themetal M2 in the matrix improves the ion hopping conductivity by simplyenlarging the number of accessible hopping centers. Moreover, thesolubility of the metal M3 is also believed to be improved such that thebuild-up of localized phases, e.g. consisting of secondary metallicnanoparticles, is avoided or at least significantly reduced. Hence,undesired change of the switching behavior, especially changes of theset and reset voltages after a certain number of switching cycles issignificantly reduced and, thus, the lifetime of the device is improved.Moreover, images obtained by optical microscopy of the composition donot show any localization of the metal M3 such as metallic phasesthereof. Thus, the presence of the metal M2 increases the solubility ofthe metal M3 in the matrix preventing the formation of such phases.

BRIEF DESCRIPTION OF THE DRAWING

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawing. Included in thedrawing are the following figures:

FIG. 1 shows the XRD curve of Comparative Example (sample) 3; and

FIG. 2 shows the XRD curve of Inventive Example (sample) 6.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention the term “metal” generally denotes the elementsof the periodic table except hydrogen, the noble gases, the halogenides,B, C, N, O, P, S, Se and Te.

The valence states of M1, M2 and M3 are all positive. Thus, in anembodiment of the composition according to the present invention themetal is present in cationic form.

The metals M1, M2 and M3 are different. In the present invention thisdenotes that M1, M2 and M3 are each based on a different element of theperiodic table.

As outlined above, the matrix comprises a metal oxide, metal sulphideand/or metal selenide as the matrix, the metal oxide, metal sulphideand/or metal selenide comprising at least two metals M1 and M2 and theatomic ratio of M1 to M2 is within the range of 75:25 to 99.99:0.01,preferably 90:10 to 99.99:0.01.

The matrix is a metal oxide, metal sulphide and/or metal selenide of themetal M1 wherein the metal M2 partially substitutes the metal M1. Due tothe lower valence state of M2 compared with M1 localized negative chargeresults. This negative localized charge is believed to improve themobility of the metal M3 and stabilizes its oxidation state.

The metal M3 is mobile in the matrix. Usually, the ratio of thediffusion coefficient of M3 to the diffusion coefficient of M2 is atleast 1000:1, preferably at least 10,000:1, more preferably at least100,000:1 and most preferably 1,000,000:1. The method for determiningthe diffusion coefficient is described in the experimental part below.Usually the ratio of the diffusion coefficients will not exceed 10⁸:1

Preferably the diffusion coefficient of the metal M2 at 1100° C. is1.10⁻¹⁰ cm²/s or below, more preferably 1.10⁻¹⁰ cm²/s or below and mostpreferably 1.10⁻¹² cm²/s or below.

Preferably the diffusion coefficient of the metal M3 at 1100° C. is1.10⁻⁷ cm²/s or higher, more preferably 5.10⁻⁶ cm²/s or higher and mostpreferably 1.10⁻⁵ cm²/s or higher.

The method for determining the diffusion coefficient is described indetail in the experimental part below.

The composition is preferably essentially free of alkaline metals andalkaline-earth metals. In the present invention “essentially free ofalkaline metals and alkaline-earth metals” denotes that the totalconcentration of alkaline metals and alkaline-earth metals is below 100ppm, based on the total weight of the composition.

Preferably, the total concentration of metals different from M1, M2 andM3 is below 100 ppm, based on the total weight of the composition.

As outlined above, the valence state of M2 is equal to or larger thanthe valence state of M3, preferably, the valence state of M2 is largerthan the valence state of M3.

Preferably, the valence state of M1 is +III, +IV or +V, preferably +IV.

The valence state of M2 is lower than the valence state of M1.Preferably the valence state of M2 is +I to +III, more preferably +II or+III and most preferably +III.

Preferably the valence state of M3 is +I to +III, more preferably +I or+II.

In one embodiment, the valence state of M1 is +V, the valence state ofM2 is +III or +IV and the valence state of M3 is +I to +III.

In another embodiment, the valence state of M1 is +IV, the valence stateof M2 is +II or +III and the valence state of M3 is +I or +II.

In yet another, preferred embodiment the valence state of M1 is +IV, thevalence state of M2 is +III and the valence state of M3 is +I or +II.

Preferably, M1 is selected from Si, Hf, Ta, Zr, Ti, Al, W and Ge, morepreferably from Si, Ta, Al, W and Ge, even more preferably from Si andTa and most preferably M1 is Si.

Preferably M2 is selected from the group consisting of B, Al, Ga, In,Tl, Sc, Y, La, Ac or mixtures thereof, preferably Al, Ga, and/or In andmost preferably is selected from Al and/or Ga.

As outlined above, the metal M2 may also be a mixture of two or moremetals, although M2 being a single metal is preferred.

M3 is preferably selected from the group consisting of Ag and Cu, and ismost preferably Cu.

The atomic ratio of M1 to M2 is within the range of 75:25 to 99.99:0.01,preferably 90:10 to 99.99:0.01, more preferably within the range of95.0:5.0 to 99.9:0.10, even more preferably within the range of 96.0:4.0to 99.0:1.0.

Preferably,

-   -   the amount of M2 is 0.01 to 25 atom % based on the entirety of        metals present in the composition; and/or    -   the amount of M3 is 0.01 to 10 atom % based on the entirety of        metals present in the composition;        more preferably,    -   the amount of M2 is 0.1 to 10.0 atom % based on the entirety of        metals present in the composition; and/or    -   the amount of M3 is 0.1 to 8.0 atom % based on the entirety of        metals present in the composition;        even more preferably,    -   the amount of M2 is 1.0 to 5.0 atom % based on the entirety of        metals present in the composition; and/or    -   the amount of M3 is 1.0 to 4.0 atom % based on the entirety of        metals present in the composition.

Preferably,

-   -   the amount of M2 is 0.01 to 25 atom % based on the entirety of        metals present in the composition; and    -   the amount of M3 is 0.01 to 10 atom % based on the entirety of        metals present in the composition;        more preferably,    -   the amount of M2 is 0.1 to 10.0 atom % based on the entirety of        metals present in the composition; and    -   the amount of M3 is 0.1 to 8.0 atom % based on the entirety of        metals present in the composition;        even more preferably,    -   the amount of M2 is 1.0 to 5.0 atom % based on the entirety of        metals present in the composition; and    -   the amount of M3 is 1.0 to 4.0 atom % based on the entirety of        metals present in the composition.

In a preferred variant of the present invention the compositioncomprises

-   (iii) a matrix comprising a metal oxide as the matrix, the matrix    comprising two metals M1 and M2, M1 being Si;-   (iv) a metal M3 which is mobile in the matrix    wherein    -   the atomic ratio of M1 to M2 is within the range of 75:25 to        99.99:0.01, preferably 90:10 to 99.99:0.01;    -   the valence states of M1, M2 and M3 are all positive;    -   the valence state of M1 is +IV;    -   the valence state of M2 is +III or below;    -   the valence state of M2 is equal to or larger than the valence        state of M3; and    -   the metals M1, M2 and M3 are different.

In the following preferred features of this variant are described.

In this variant the matrix is formed of amorphous or crystalline silicondioxide, preferably amorphous silicon dioxide with the metal M2partially replacing the silicon atoms.

The metal M3 is mobile in the matrix. Usually, the ratio of thediffusion coefficient of M3 to the diffusion coefficient of M2 is atleast 1000:1, preferably at least 10,000:1, more preferably at least100,000:1 and most preferably 1,000,000:1. The method for determiningthe diffusion coefficient is described in the experimental part below.Usually the ratio of the diffusion coefficients will not exceed 10⁸:1.

Preferably the diffusion coefficient of the metal M2 at 1100° C. is1.10⁻¹⁰ cm²/s or below, more preferably 1.10⁻¹⁰ cm²/s or below and mostpreferably 1.10⁻¹² cm²/s or below.

Preferably the diffusion coefficient of the metal M3 at 1100° C. is1.10⁻⁷ cm²/s or higher, more preferably 5.10⁻⁶ cm²/s or higher and mostpreferably 1.10⁻⁵ cm²/s or higher.

The method for determining the diffusion coefficient is described indetail in the experimental part below.

The composition is preferably essentially free of alkaline metals andalkaline-earth metals. In the present invention “essentially free ofalkaline metals and alkaline-earth metals” denotes that the totalconcentration of alkaline metals and alkaline-earth metals is below 100ppm, based on the total weight of the composition.

Preferably the total concentration of metals different from M1, M2 andM3 is below 100 ppm, based on the total weight of the composition.

As outlined above, the valence state of M2 is equal to or larger thanthe valence state of M3, preferably, the valence state of M2 is largerthan the valence state of M3.

Preferably the valence state of M2 is +I to +III, more preferably +II or+III and most preferably +III.

Preferably the valence state of M3 is +I to +III, more preferably +I or+II.

Preferably the valence state of M2 is +III and the valence state of M3is +I or +II.

Preferably M2 is selected from the group consisting of B, Al, Ga, In,Tl, Sc, Y, La or Ac, preferably Al, Ga, and/or In and most preferably isselected from Al and/or Ga.

M3 is preferably selected from the group consisting of Ag and Cu, and ismost preferably Cu.

In one embodiment of this variant, M2 is selected from the groupconsisting of Al, Ga, and/or In and M3 is Cu.

The atomic ratio of M1 to M2 is within the range of 75:25 to 99.99:0.01,more preferably 90:10 to 99.99:0.01, preferably within the range of95.0:5.0 to 99.9:0.10, more preferably within the range of 96.0:4.0 and99.0:1.0.

Preferably,

-   -   the amount of M2 is 0.01 to 25 atom % based on the entirety of        metals present in the composition; and/or    -   the amount of M3 is 0.01 to 10 atom % based on the entirety of        metals present in the composition;        more preferably,    -   the amount of M2 is 0.1 to 10.0 atom % based on the entirety of        metals present in the composition; and/or    -   the amount of M3 is 0.1 to 8.0 atom % based on the entirety of        metals present in the composition;        even more preferably,    -   the amount of M2 is 1.0 to 5.0 atom % based on the entirety of        metals present in the composition; and/or    -   the amount of M3 is 1.0 to 4.0 atom % based on the entirety of        metals present in the composition.

Preferably,

-   -   the amount of M2 is 0.01 to 25 atom % based on the entirety of        metals present in the composition; and    -   the amount of M3 is 0.01 to 10 atom % based on the entirety of        metals present in the composition;        more preferably,    -   the amount of M2 is 0.1 to 10.0 atom % based on the entirety of        metals present in the composition; and    -   the amount of M3 is 0.1 to 8.0 atom % based on the entirety of        metals present in the composition;        and most preferably,    -   the amount of M2 is 1.0 to 5.0 atom % based on the entirety of        metals present in the composition; and    -   the amount of M3 is 1.0 to 4.0 atom % based on the entirety of        metals present in the composition.

In the following preferred features of various embodiments of theinvention are described unless explicitly stated to the contrary.

In one embodiment

-   -   M1 is selected from Si, Ta, Zr, Ti, Al, W and Ge, more        preferably from Si, Ta, Zr and Ti and most preferably M1 is Si;    -   M2 is selected from the group consisting of B, Al, Ga, In, Tl,        Sc, Y, La, Ac or mixtures thereof, preferably Al, Ga, and/or In        and most preferably is selected from Al and/or Ga; and    -   M3 is selected from the group consisting of Ag and Cu, and is        most preferably is Cu.

In another embodiment

-   -   M1 is selected from Si, Ta, Zr and Ti and most preferably M1 is        Si;    -   M2 is selected from the group consisting of Al, Ga, and/or In        and most preferably is selected from Al and/or Ga; and    -   M3 is selected from the group consisting of Ag and/or Cu and is        most preferably is Cu.

In yet another embodiment

-   -   M1 is Si;    -   M2 is Al; and    -   M3 is Cu.

In one further variant

-   -   M1 is selected from Si, Ta, Zr, Ti, Al, W and Ge, more        preferably from Si, Ta, Zr and Ti and most preferably M1 is Si;    -   M2 is selected from the group consisting of B, Al, Ga, In, Tl,        Sc, Y, La, Ac or mixtures thereof, preferably Al, Ga, and/or In        and most preferably is selected from Al and/or Ga; and    -   M3 is selected from the group consisting of Ag and Cu, and is        most preferably is Cu;        the total concentration of metals different from M1, M2 and M3        is below 100 ppm, based on the total weight of the composition        and    -   the amount of M2 is 0.01 to 25 atom % based on the entirety of        metals present in the composition; and/or, preferably and    -   the amount of M3 is 0.01 to 10 atom % based on the entirety of        metals present in the composition;        more preferably,    -   the amount of M2 is 0.1 to 10.0 atom % based on the entirety of        metals present in the composition; and/or, preferably and    -   the amount of M3 is 0.1 to 8.0 atom % based on the entirety of        metals present in the composition;        even more preferably,    -   the amount of M2 is 1.0 to 5.0 atom % based on the entirety of        metals present in the composition; and/or, preferably and    -   the amount of M3 is 1.0 to 4.0 atom % based on the entirety of        metals present in the composition.

In another variant

-   -   M1 is selected from Si, Ta, Zr and Ti and most preferably M1 is        Si;    -   M2 is selected from the group consisting of Al, Ga, and/or In        and most preferably is selected from Al and/or Ga; and    -   M3 is selected from the group consisting of Ag and/or Cu and is        most preferably is Cu        the total concentration of metals different from M1, M2 and M3        is below 100 ppm, based on the total weight of the composition        and    -   the amount of M2 is 0.01 to 25 atom % based on the entirety of        metals present in the composition; and    -   the amount of M3 is 0.01 to 10 atom % based on the entirety of        metals present in the composition;        more preferably,    -   the amount of M2 is 0.1 to 10.0 atom % based on the entirety of        metals present in the composition; and    -   the amount of M3 is 0.1 to 8.0 atom % based on the entirety of        metals present in the composition;        even more preferably,    -   the amount of M2 is 1.0 to 5.0 atom % based on the entirety of        metals present in the composition; and    -   the amount of M3 is 1.0 to 4.0 atom % based on the entirety of        metals present in the composition.

In yet another variant

-   -   M1 is Si;    -   M2 is Al; and    -   M3 is Cu;        the total concentration of metals different from M1, M2 and M3        is below 100 ppm, based on the total weight of the composition        and    -   the amount of M2 is 0.1 to 10.0 atom % based on the entirety of        metals present in the composition; and    -   the amount of M3 is 0.1 to 8.0 atom % based on the entirety of        metals present in the composition;        preferably,    -   the amount of M2 is 1.0 to 5.0 atom % based on the entirety of        metals present in the composition; and    -   the amount of M3 is 1.0 to 4.0 atom % based on the entirety of        metals present in the composition.

The present invention is furthermore directed to a process for theproduction of the composition according to the invention, preferably theprocess comprises the following steps

-   g) providing a porous oxide, sulphide or selenide of M1;-   h) infiltrating the porous oxide, sulphide or selenide of M1 with a    liquid precursor of M2;-   i) infiltrating the porous oxide, sulphide or selenide of M1 with a    liquid precursor of M3;    whereby steps b) and c) may be carried out simultaneously or    subsequently;-   j) optionally drying the product obtained after infiltrating the    porous oxide, sulphide or selenide of M1 with the liquid precursor    of M2 and the liquid precursor of M3;-   k) optionally calcining the product obtained in step d), if present,    or step c) in an oxidizing atmosphere at a temperature below the    transition temperature of the oxide, sulphide or selenide of M1;-   l) heating the product obtained in step e), if present, step d), if    present or step c) to a temperature above the transition temperature    of the oxide, sulphide or selenide of M1.

In this regard the “transition temperature” denotes the temperature atwhich a material changes from one state to another, usually from a solidstate to a viscous state, e.g. liquid state, or vice versa. Preferablythe material is heated above the glass transition temperature or abovethe melting temperature of the oxide, sulphide or selenide of M1.

Steps a), b) and c) are usually carried out at 0 to 25° C., but may beperformed at elevated temperatures also, e.g. 0 to 50° C. In some casesit may be advised to perform steps a), b) and c) at temperatures below25° C., such as below 15° C., e.g. in case steps a), b) and/or c) arecompleted under sub-atmospheric pressure.

Drying step d), if present, is usually carried out at a temperature ofabove 25° C. but below the transition temperature of the oxide, sulphideor selenide of M1, such as 50° C. to 400° C.

Steps a) to c) and d), if present, may be carried out at atmosphericpressure or sub-atmospheric pressure and are preferably carried out atsub-atmospheric pressure, e.g. in a rotary evaporator at sub-atmosphericpressure.

In the present invention atmospheric pressure denotes a pressure of 1013mbar.

Step e) if present, is usually carried out at a temperature of 500 to1000° C.

The oxidizing atmosphere in step e), if present, is usually air, oxygenor other oxygen-containing gases.

Step f) is usually carried out under sub-atmospheric pressure,preferably under vacuum, such as 20 mbar or below.

The composition as obtained above can for example be used as asputtering target for physical vapor deposition (PVD) processes.

Alternatively the composition may be prepared by atomic layer deposition(ALD) or chemical vapor deposition (CVD). These methods are generallyknown in the art.

In case the composition is deposited layer by layer, e.g. by atomiclayer deposition, the applied layers may comprise only one of the metalsM1, M2 or M3 or the applied layers may comprise a mixture of two or moreof M1, M2 and M3.

Applying layers only comprising one of the metals M1, M2 or M3 isusually preferred. Thereby side reactions between the precursors of themetals M1, M2 and M3 cannot take place. Moreover, in a mixture of two ormore metal precursors the precursor of one of the metals may betterphysio- and chemisorb with the surface than the precursor of the othermetal and, thus, the layer composition, i.e. content of the individualmetals, is not identical to the content in the reactant mixture.

In case layers only comprising one of the metals M1, M2 or M3 areapplied subsequently the desired concentration in the composition can beeasily achieved by selecting the number of the respective layersappropriately.

In either case usually an annealing step is performed after all layersof the composition are applied thereby forming the composition accordingto the invention. It is also possible to apply some of the layers of thecomposition, perform an annealing step and then apply further layer(s)of the composition then perform another annealing step until all layersof the composition are applied. However, applying all layers andperforming a single annealing step thereafter is preferred.

The annealing step, if present, is usually performed at a temperaturelower than the transition temperature of the oxide, sulphide or selenideof M1.

In this regard the “transition temperature” denotes the temperature atwhich a material changes from one state to another, usually from a solidstate to a viscous state, e.g. liquid state, or vice versa. Preferablythe material is heated to the glass transition temperature or meltingtemperature of the oxide, sulphide or selenide of M1.

The thickness of the layer is usually 1 to 100 nm, preferably 5 to 10nm.

Preferred features of the composition of the present invention are alsopreferred features of the process of the present invention and viceversa.

The present invention is furthermore directed to the use of thecomposition according to the present invention or obtained in theprocesses of the present invention as a resistive switching element,e.g. in a resistive switching memory such as a resistive switchingmemory cell based on electrochemical metallization (ECM).

Due to the purity obtainable in the composition according to the presentinvention, the degradation is negligible. Thus, the composition of thepresent invention may alternatively be used as an active core in fiberlaser applications or as wavelength conversion lamp tubing, e.g. forflash lamps, especially, UV→VIS for pump flash lamps, particularly forgreen luminescence.

Preferred features of the composition and the process of the presentinvention are also preferred features of the use according to thepresent invention and vice versa.

EXAMPLES

The invention will now be described with the following non-limitingexamples.

Experimental Part

Measurement Methods

Diffusion Coefficient of M2 and M3

The method is performed analogous to the method described by Gunther H.Frischat, in Sodium Diffusion in SiO ₂ Glass, Journal of The AmericanCeramic Society, Vol 51, No. 9, 1968, p. 528-530.

The sample was prepared by applying the solution of a radioactive tracerof the metal to be determined onto a polished glass specimen (size 10mm·10 mm) of Heraeus Infrasil 302® and a second glass specimen ofHeraeus Infrasil 302® was applied on top thereof, thereby obtaining asandwiched structure. Thereafter the specimen was heated to 1100° C. inan oven for an appropriate time. The further procedure was as describedin the above paper of Frischat items (2) and (3).

Suitable tracers are known in the art, e.g. 65 Cu or 26 Al.

Transition Temperature, Glass Transition Temperature, MeltingTemperature

Determination of Glass Transition Temperature Tg (Glass)

The glass transition temperature Tg for glasses is determined using aDSC apparatus Netzsch STA 449 F3 Jupiter (Netzsch) equipped with asample holder HTP 40000A69.010, thermocouple Type S and a platinum ovenPt S TC:S (all from Netzsch). For the measurements and data evaluationthe measurement software Netzsch Messung V5.2.1 and Proteus ThermalAnalysis V5.2.1 are applied. As pan for reference and sample, aluminumoxide pan GB 399972 and cap GB 399973 (both from Netzsch) with adiameter of 6.8 mm and a volume of about 85 μl are used. An amount ofabout 20-30 mg of the sample is weighed on the sample pan with anaccuracy of 0.01 mg. The empty reference pan and the sample pan areplaced in the apparatus, the oven is closed and the measurement started.A heating rate of 10 K/min is employed from a starting temperature of25° C. to an end temperature of 1000° C. The balance in the instrumentis always purged with nitrogen (N₂ 5.0 nitrogen gas with quality 5.0which represents a purity of 99.999%) and the oven is purged withsynthetic air (80% N₂ and 20% O₂ from Linde) with a flow rate of 50ml/min. The first step in the DSC signal is evaluated as glasstransition using the software described above and the determined onsetvalue is taken as the temperature for Tg.

The melting temperature T_(m) is determined in an analogous mannerwhereby the maximum in the DSC-signal is evaluated as the meltingtemperature T_(m).

Metal Content (of M1, M2, M3, Alkaline and Alkaline Earth Metals etc.)

The determination was carried out using a Varian Vista MPX ICP-OESinstrument (available from Varian Inc.). The system was calibrated usingtwo reference solutions with known metal content in a 3:1 mixture ofhydrofluoric acid (40 wt. %) and nitric acid (60 wt. %).

The settings of the Varian Vista MPX ICP-OES instrument were as follows.

-   Power settings: 1.25 kW-   plasma: 15.0 l/min (Argon)-   auxiliary gas: 1.50 l/min (Argon)-   atomizer pressure: 220 kPa (Argon)-   repetitions: 20 s-   equilibration time: 45 s-   observation height: 10 mm-   suction time: 45 s-   purging time: 10 s-   pumping speed: 20 rpm-   repetitions: 3

0.10±0.02 g of the sample are combined with 3 ml nitric acid and 9 mlhydrofluoric acid and heated in an Anton Paar Multiwave 3000 microwaveoven at 800 to 1200 W for 60 minutes. The sample is introduced into a100 ml volumetric flask using hydrochloric acid (50 Vol. %) and used forthe measurement.

XRD Measurement

In an air conditioned room with a temperature of 22±1° C. equipment andmaterials are equilibrated prior the measurement. Crystallinitymeasurements were performed using a “STOE Stadi P” from STOE & Cie GmbH,Darmstadt, Germany, equipped with a CuK_(α1) (0.154056 nm) x-ray source,a curved Ge single crystal (111) monochromator, with transmissionequipment (detector: linear PSD (position sensitive detector) fromSTOE), a generator “Seifert ISO-DEBYEFLEX 3003” from GE Sensing andinspection Technologies GmbH (40 kV, 40 mA) and the software “STOEPowder Diffraction Software (win x-pow) Version 3.05” from STOE. Thisdevice applies the x-ray scattering measuring principle. Calibration ofthe device is in accordance with the NIST-standard Si (lot number: 640c). As reference for the analysis the ICDD database is applied. Thesample is placed in a quantity in order to achieve a thin film betweentwo foils (comes with the sample holder from STOE) in the middle of thesample holder prior to placing it in the x-ray beam. The sample wasmeasured in a transmission mode at 22° C. with the following parameters:2θ: 3.0-99.8°, ω: 1.5-49.9°, step: 2θ 0.55°, ω: 0.275°, step time: 20 s,measure time: 1.03 h. When plotting 2θ versus intensity using theequipped software package, the presence of peaks representingcrystalline material can be detected.

Particles Size Determination Using Laser Scattering

For particle size determination of the particles a laser diffractionmethod was used according to ISO Standard 13320. A Mastersizer 3000 fromMalvern equipped with a He—Ne Laser and a blue LED and wet dispersingunit has been employed for the measurements performed at roomtemperature of 23° C. The conditions of the wet dispersion unit were setto 80% ultrasonic power before measurement and as a dispersant water wasused. The values for d₁₀, d₅₀, d₉₀ were determined using the Malvernsoftware 21 CFR, a form factor of 1 and the Fraunhofer theory.

Porosity and Pore Size by Hg Porosimetry

Mercury porosimetry analysis was performed according to ISO15901-1(2005). A ThermoFisher Scientific PASCAL 140 (low pressure up to 4 bar)und a PASCAL 440 (high pressure up to 4000 bar) and SOLID Version 1.3.3(Aug. 2, 2012) software (all from ThermoFisher Scientific) werecalibrated with porous glass spheres with a pore diameter of 75 nm(University of Leipzig, Fakultät für Chemie und Mineralogie, Institutfür Technische Chemie). During measurements the pressure was increasedor decreased continuously and controlled automatically by the instrumentrunning in the PASCLA mode and speed set to 6 for intrusion and 8 forextrusion. The Washburn method was employed for the evaluation and thedensity of Hg was corrected for the actual temperature. The value forsurface tension was 0.484 N/m and contact angle 141.1°. The sample sizewas between about 30 and 40 mg. Before starting a measurement sampleswere heated to 120° C. for 24 hours. Evacuation is performedautomatically by the instrument for 10 minutes to an absolute pressureof 0.01 kPa.

Used Materials

Amorphous SiO₂ pyrogenic silica is slurried in deionized water and driedin a drying tower at a temperature of >100° C. thereby obtaining poroussilica having a particle size (d₅₀) of about 100-500 μm with an innerpore volume of about 0.7 ml/g Al precursor anhydrous AlCl₃ obtained fromAlfa Aesar Cu precursor anhydrous CuSO₄ obtained from Alfa Aesar

The compositions have been prepared by infiltration of mixed solutioninto the inner porosity of porous silica particles as follows. Theproperties are shown in table 1 below.

Comparative Example 1 (CE1)

0.133 g CuSO₄ are added to a round-bottomed flask and dissolved indeionized water. To this solution 500 g of the porous SiO₂ as definedabove are added and shaken until the mixture shows Newtonian behavior.Subsequently the mixture is dried at 130° C. on a rotary evaporatoruntil a dry powder is obtained. The powder is transferred to analuminium bowl and dried for 48 h in a drying oven at 150° C. Thereafterthe residual humidity is determined and the sample cooled to roomtemperature (25° C.).

Thereafter the resulting product was heated to 1700° C. under a vacuumof 5 mbar for melting.

Comparative Example 2 (CE2)

Comparative example 1 has been repeated whereby 1.33 g CuSO₄ have beenused.

Comparative Example 3 (CE3)

Comparative example 1 has been repeated whereby 13.3 g CuSO₄ have beenused.

Inventive Example 4 (IE4)

The procedure of comparative example 1 has been repeated whereby 0.133 gCuSO₄ is added to a round-bottomed flask and dissolved in deionizedwater. 0.166 g AlCl₃ are carefully added. To this solution 500 g of theporous SiO₂ as defined above are added and the procedure of comparativeexample 1 has been repeated.

The properties are shown in table 1 below.

Inventive Example 5 (IE5)

Inventive example 4 has been repeated whereby 1.33 g CuSO₄ and 1.66 gAlCl₃ as prepared above have been used.

Inventive Example 6 (IE6)

Inventive example 4 has been repeated whereby 13.3 g CuSO₄ and 16.6 gAlCl₃ as prepared above have been used.

TABLE 1 Appearance Cu [ppm]¹⁾ Al [ppm]¹⁾ CE1 slightly red, noinhomogeneity visible 135 8²⁾ CE2 individual, separated areas of high1270 1²⁾ Cu-concentration visible under the microscope CE3 individual,separated areas of high 10102 0  Cu-concentration visible under themicroscope IE4 no individual areas as in case of 169 148   CE2 and CE3visible IE5 no individual areas as in case of 1213 1485   CE2 and CE3visible IE6 no individual areas as in case of 11014 14067    CE2 and CE3visible ¹⁾determined in powder form ²⁾The minimal Al-content resultsfrom impurities due to handlingXRD Measurement

FIG. 1 shows the XRD curve of sample 3 and FIG. 2 the XRD curve ofsample 6. As can be seen from the curves, intensities of the peaks areat about 43.5 2Theta, 50.5 2Theta and 74.0 2Theta and the intensities ofinventive sample 6 are significantly lower. These peaks indicate thepresence of crystalline metallic copper phases having a size of 100 to250 nm. Thus, inventive sample 6 has nearly no such phases albeit thecopper content is higher compared with comparative example 3.

The invention claimed is:
 1. A composition comprising: a matrix comprising a metal oxide as the matrix material, the metal oxide comprising at least two metals M1 and M2, and a metal M3 which is mobile in the matrix, wherein the atomic ratio of M1 to M2 is within the range of 75:25 to 99.99:0.01; the valence states of M1, M2 and M3 are all positive; the valence state of M1 is larger than the valence state of M2; the valence state of M2 is equal to or larger than the valence state of M3; and the metals M1, M2 and M3 are different, wherein M1 is Si or Ge, M2 is selected from the group consisting of Al, Ga, In, Tl, Sc, Y, La, Ac or mixtures thereof, and M3 is selected from the group consisting of Ag or Cu, and wherein the total concentration of metals different from M1, M2 and M3 in the composition is below 100 ppm, based on the total weight of the composition.
 2. The composition according to claim 1, wherein M2 has a diffusion coefficient in the composition, M3 has a diffusion coefficient in the composition, and the ratio of the diffusion coefficient of M3 in the composition to the diffusion coefficient of M2 in the composition is at least 1000:1.
 3. The composition according to claim 1, wherein the valence state of M1 is +III, +IV or +V.
 4. The composition according to claim 1, wherein the amount of M2 is 0.01 to 25 atom % based on the entirety of metals present in the composition; and the amount of M3 is 0.01 to 10 atom % based on the entirety of metals present in the composition.
 5. The composition according to claim 1 wherein the atomic ratio of M1 to M2 is within the range of 90:10 to 99.99:0.01.
 6. The composition according to claim 1 wherein M2 is selected from the group consisting of Al or Ga.
 7. The composition according to claim 1 wherein M3 is Cu.
 8. A process for the production of a composition comprising a matrix comprising one or more of a metal oxide, metal sulphide or metal selenide as the matrix material, the metal oxide, metal sulphide or metal selenide comprising at least two metals M1 and M2, and a metal M3 which is mobile in the matrix, wherein the atomic ratio of M1 to M2 is within the range of 75:25 to 99.99:0.01; the valence states of M1, M2 and M3 are all positive; the valence state of M1 is larger than the valence state of M2; the valence state of M2 is equal to or larger than the valence state of M3; and the metals M1, M2 and M3 are different, the process comprising the following steps: a) providing a porous oxide, sulphide or selenide of M1; b) infiltrating the porous oxide, sulphide or selenide of M1 with a liquid precursor of M2; c) infiltrating the porous oxide, sulphide or selenide of M1 with a liquid precursor of M3; whereby steps b) and c) are carried out simultaneously or subsequently; d) optionally drying the product obtained after infiltrating the porous oxide, sulphide or selenide of M1 with the liquid precursor of M2 and the liquid precursor of M3; e) optionally calcining the product obtained in step d), if present, or step c) in an oxidizing atmosphere at a temperature below the transition temperature of the oxide, sulphide or selenide of M1; and f) heating the product obtained in step e), if present, step d), if present or step c) to a temperature above the transition temperature of the oxide, sulphide or selenide of M1.
 9. A method of using the composition obtained by the process according to claim 8 as a sputtering target for physical vapor deposition (PVD) processes.
 10. A process for the production of a composition comprising a matrix comprising one or more of a metal oxide, metal sulphide or metal selenide as the matrix material, the metal oxide, metal sulphide or metal selenide comprising at least two metals M1 and M2, and a metal M3 which is mobile in the matrix, wherein the atomic ratio of M1 to M2 is within the range of 75:25 to 99.99:0.01; the valence states of M1, M2 and M3 are all positive, the valence state of M1 is larger than the valence state of M2; the valence state of M2 is equal to or larger than the valence state of M3; and the metals M1, M2 and M3 are different, the process comprising a step of atomic layer deposition (ALD) or chemical vapor deposition (CVD).
 11. The process of claim 10 wherein the composition is prepared by ALD and the thickness of the layer is 1 to 100 nm.
 12. A method of using a composition comprising a matrix comprising one or more of a metal oxide, metal sulphide or metal selenide as the matrix material, the metal oxide, metal sulphide or metal selenide comprising at least two metals M1 and M2, and a metal M3 which is mobile in the matrix, wherein the atomic ratio of M1 to M2 is within the range of 75:25 to 99.99:0.01; the valence states of M1, M2 and M3 are all positive; the valence state of M1 is larger than the valence state of M2; the valence state of M2 is equal to or larger than the valence state of M3; and the metals M1, M2 and M3 are different as a resistive switching element.
 13. A composition comprising: a matrix comprising a metal oxide as the matrix material, the metal oxide comprising at least two metals M1 and M2, and a metal M3 which is mobile in the matrix, wherein the atomic ratio of M1 to M2 is within the range of 75:25 to 99.99:0.01; the valence states of M1, M2 and M3 are all positive; the valence state of M1 is +III, +IV or +V and is larger than the valence state of M2; the valence state of M2 is equal to or larger than the valence state of M3; the metals M1, M2 and M3 are different, with M1 being selected from Si or Ge, M2 being selected from the group consisting of Al, Ga, In, Tl, Sc, Y, La, Ac or mixtures thereof, and M3 being selected from the group consisting of Ag or Cu; the ratio of the diffusion coefficient of M3 in the composition to the diffusion coefficient of M2 in the composition is at least 1000:1; the total concentration of alkaline metals and alkaline-earth metals is below 100 ppm, based on the total weight of the composition; the amount of M2 is 0.01 to 25 atom % based on the entirety of metals, present in the composition; and the amount of M3 is 0.01 to 10 atom % based on the entirety of metals present in the composition.
 14. A composition comprising: a matrix comprising a metal oxide as the matrix material, the metal oxide comprising at least two metals M1 and M2, and a metal M3 which is mobile in the matrix, wherein the atomic ratio of M1 to M2 is within the range of 90:10 to 99.99:0.01; the valence states of M1, M2 and M3 are all positive; the valence state of M1 is +III, +IV or +V and is larger than the valence state of M2; the valence state of M2 is equal to or larger than the valence state of M3; the metals M1, M2 and M3 are different, with M1 being Si, M2 being selected from the group consisting of Al or Ga, and M3 is Cu; the ratio of the diffusion coefficient of M3 in the composition to the diffusion coefficient of M2 in the composition is at least 1000:1; the total concentration of alkaline metals and alkaline-earth metals is below 100 ppm, based on the total weight of the composition; the amount of M2 is 0.01 to 25 atom % based on the entirety of metals present in the composition; and the amount of M3 is 0.01 to 10 atom % based on the entirety of metals present in the composition. 